1. Field of the Invention
The present invention relates generally to a receiver, and more particularly is directed to a receiver that includes a circuit to control the pass band of a demodulated signal.
2. Description of the Prior Art
In prior art radio receivers when the electric field intensity of a received broadcasting wave is low, noise components of relatively high frequency are included in sound reproduced from the speaker. As a result, the reproduced sound is less intelligible or is less pleasant to listen to or both. This is caused by the fact that an intermediate frequency amplifier stage or low frequency amplifier stage has a fixed pass band.
It has already been proposed to control the pass band of the intermediate frequency signal stage in response to the electric field intensity of the desired signal. The intermediate frequency stage was designed to have a pass band of a certain width in response to a strong signal but to have a narrower pass band in response to a weak signal. Accordingly, noise contained in the high frequency band components of the demodulated signal was partially eliminated when a weak signal was being received, but the improvement in the signal-to-noise (S/N) ratio was not good enough.